This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Heme is the greatest source of essential iron for pathogens residing within a host. However, the iron is sequestered by the host to prevent its misuse by invading bacteria. Therefore, pathogens have evolved high affinity uptake systems that can specifically recognize and take up host heme. The Isd (iron surface determinant) family of proteins from Staphylococcus aureus and the Cha (Campylobacter heme acquisition) proteins from Campylobacter jejuni are components of characterized heme transport systems. The structural basis for understanding the molecular mechanism of these transport systems is still lacking. Data collected recently on ChaN at the SSRL has been used to determine the structure of the heme-bound protein, which demonstrates a novel model of heme dependent dimerization. Crystal structures of mutants of ChaN will be determined to probe the role of specific residues in heme-dependent dimerization and in interaction with other Cha transport components. Preliminary crystals of a heme binding domains of Isd proteins have been produced and will be optimized for high-resolution structure determination.